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Teach InstCombine to work with smaller legal types in icmp (shl %v, C1), C2

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It enables to work with a smaller constant, which is target friendly for those which can compare to immediates.
It also avoids inserting a shift in favor of a trunc, which can be free on some targets.

This used to work until LLVM-3.1, but regressed with the 3.2 release.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@175270 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Arnaud A. de Grandmaison 2013-02-15 14:35:47 +00:00
parent 85d2760c8e
commit 7c5c9b39c9
3 changed files with 61 additions and 3 deletions
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19
lib/Transforms/InstCombine/InstCombineCompares.cpp
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@ -1331,6 +1331,25 @@ Instruction *InstCombiner::visitICmpInstWithInstAndIntCst(ICmpInst &ICI,
return new ICmpInst(TrueIfSigned ? ICmpInst::ICMP_NE : ICmpInst::ICMP_EQ,
And, Constant::getNullValue(And->getType()));
}
// Transform (icmp pred iM (shl iM %v, N), CI)
// -> (icmp pred i(M-N) (trunc %v iM to i(N-N)), (trunc (CI>>N))
// Transform the shl to a trunc if (trunc (CI>>N)) has no loss.
// This enables to get rid of the shift in favor of a trunc which can be
// free on the target. It has the additional benefit of comparing to a
// smaller constant, which will be target friendly.
unsigned Amt = ShAmt->getLimitedValue(TypeBits-1);
if (Amt != 0 && RHSV.countTrailingZeros() >= Amt) {
Type *NTy = IntegerType::get(ICI.getContext(), TypeBits - Amt);
Constant *NCI = ConstantExpr::getTrunc(
ConstantExpr::getAShr(RHS,
ConstantInt::get(RHS->getType(), Amt)),
NTy);
return new ICmpInst(ICI.getPredicate(),
Builder->CreateTrunc(LHSI->getOperand(0), NTy),
ConstantExpr::getTrunc(NCI, NTy));
}
break;
}

7
test/Transforms/InstCombine/exact.ll
View File

@ -99,9 +99,9 @@ define i1 @ashr_icmp2(i64 %X) nounwind {
; PR9998
; Make sure we don't transform the ashr here into an sdiv
; CHECK: @pr9998
; CHECK: = and i32 %V, 1
; CHECK: %Z = icmp ne
; CHECK: ret i1 %Z
; CHECK: [[BIT:%[A-Za-z0-9.]+]] = and i32 %V, 1
; CHECK-NEXT: [[CMP:%[A-Za-z0-9.]+]] = icmp ne i32 [[BIT]], 0
; CHECK-NEXT: ret i1 [[CMP]]
define i1 @pr9998(i32 %V) nounwind {
entry:
%W = shl i32 %V, 31
@ -112,6 +112,7 @@ entry:
}
; CHECK: @udiv_icmp1
; CHECK: icmp ne i64 %X, 0
define i1 @udiv_icmp1(i64 %X) nounwind {

38
test/Transforms/InstCombine/icmp.ll
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@ -706,3 +706,41 @@ define i1 @test69(i32 %c) nounwind uwtable {
%3 = or i1 %1, %2
ret i1 %3
}
; CHECK: @icmp_sext16trunc
; CHECK-NEXT: %1 = trunc i32 %x to i16
; CHECK-NEXT: %cmp = icmp slt i16 %1, 36
define i1 @icmp_sext16trunc(i32 %x) {
%trunc = trunc i32 %x to i16
%sext = sext i16 %trunc to i32
%cmp = icmp slt i32 %sext, 36
ret i1 %cmp
}
; CHECK: @icmp_sext8trunc
; CHECK-NEXT: %1 = trunc i32 %x to i8
; CHECK-NEXT: %cmp = icmp slt i8 %1, 36
define i1 @icmp_sext8trunc(i32 %x) {
%trunc = trunc i32 %x to i8
%sext = sext i8 %trunc to i32
%cmp = icmp slt i32 %sext, 36
ret i1 %cmp
}
; CHECK: @icmp_shl16
; CHECK-NEXT: %1 = trunc i32 %x to i16
; CHECK-NEXT: %cmp = icmp slt i16 %1, 36
define i1 @icmp_shl16(i32 %x) {
%shl = shl i32 %x, 16
%cmp = icmp slt i32 %shl, 2359296
ret i1 %cmp
}
; CHECK: @icmp_shl24
; CHECK-NEXT: %1 = trunc i32 %x to i8
; CHECK-NEXT: %cmp = icmp slt i8 %1, 36
define i1 @icmp_shl24(i32 %x) {
%shl = shl i32 %x, 24
%cmp = icmp slt i32 %shl, 603979776
ret i1 %cmp
}